R1100RS Transmission

[jerryjameson]

Hello All,
Here's my question, If I may indulge y'all,
I have a 94 R1100RS with 60K on her. The transmission (M94) Shifts fine but will produce a substantial 'klunk' moving from first to second. Only a soft hand on the throttle will avoid the lurking jolt. I understand that this situation, quite manageable now, can only go to bad and then worse over time. The question, what if anything can prolong the life of this box?
I am presently establishing a 'save the transmission fund'.

Thanks,

Jerry

[breyfogle]

The first $0.02 to your M94 fund:

I've read a lot of posts dealing with M94 failures and a "klunky" first to second upshift is not one of the symptoms I've read about. My RS still has its original M94 tranny, down shifts can be "klunky" is I am a bit careless with my timing but upshifts are always very smooth.

Nothin' personnel, but how's your shifting technique? M94 trannies will upshift very nicely if (1) they are shifted somewhere around 5000 RPM, (2) with a bit of preload on the shifter, and (3) minimal clutch lever (maybe 1/4 travel) movement.

[jerryjameson]

Thanks for the response,
There is no difficulty or sound during the upshift, provided the RPM rate is synced. pre-loded etc. The Clunk happens post shift when I then add throttle. If I bring the RPM up really (really!) slowly its all good, any rapid uptick and.... THUNK, big and heavy.

Whatsthatabout...you think, eh?

Jerry.

[Andy VH]

When BMW set the specs for the 94 tranny from Getrag, durability was big factor. So design choices were made for the shifting forks, followers, gear dogs that are durable but result in harsh shifting action especially in the lower gears.

My 94 R1100RS still shifts like a typical early 90s BMW even though it has a 96 spec tranny in it. Make sure your clutch is accurately adjusted (it does make a difference). The clutch hub splines (tranny input splines) HAVE to be lubed to reduce clutch/shifting force. The cltuch cable must be routed properly to minimize any tight bends.

On my R1100RS, I use synthetic gear lube GL5 spec 75W90. Because the tranny runs in its own oil supply, you can add friction modifiers with no detriment to the tranny. I added some NAPA differential friction modifier to my tranny and it does seem to shift a bit better.

The rest comes down to technique. Preload the shift lever, keep your clutch lever actuation as short (1/3 stroke) as possible, accurately match engine speed to road speed and shift timing. When it all comes together it can make decent shifts.

[kbasa]

When BMW set the specs for the 94 tranny from Getrag, durability was big factor. So design choices were made for the shifting forks, followers, gear dogs that are durable but result in harsh shifting action especially in the lower gears.

My 94 R1100RS still shifts like a typical early 90s BMW even though it has a 96 spec tranny in it. Make sure your clutch is accurately adjusted (it does make a difference). The clutch hub splines (tranny input splines) HAVE to be lubed to reduce clutch/shifting force. The cltuch cable must be routed properly to minimize any tight bends.

On my R1100RS, I use synthetic gear lube GL5 spec 75W90. Because the tranny runs in its own oil supply, you can add friction modifiers with no detriment to the tranny. I added some NAPA differential friction modifier to my tranny and it does seem to shift a bit better.

The rest comes down to technique. Preload the shift lever, keep your clutch lever actuation as short (1/3 stroke) as possible, accurately match engine speed to road speed and shift timing. When it all comes together it can make decent shifts.

+1

I use Dow Gear Guard in our 94 RS trans.

[jerryjameson]

So,
Y'all saying that it may be my shifting technique coupled with a more complex box that is creating this problem, I'm willing to entertain that idea, Its certainly more appealing than an imminent mechanical failure. In that case, a couple of things to throw into the mix,

Firstly, why has this post-shift clunk only materialized recently?
Secondly, Shifting to second at 5000RPM seems awfully high, yes,no?
and finally, are there any tell-tale signs that may indicate if the problem may be clutch related?
I'm looking into using Redline Heavyweight Shockproof
"Recommended for heavily-loaded racing differentials and transmissions,The viscosity characteristics allow the lubricant to resist throwoff and provide a film thickness similar to a 75W250 grade, while providing the same low fluid friction as an SAE 75W90."

Any Opinions, good people?

Thanks.
Jerry.

[MCMXCIVRS]

I've been using the Heavy Shookproof oil in my RS's gear box ever since replacing the original with a factory rebuilt unit (m97 spec). No ill effects experienced.

It does seem odd that you notice the clunk post shift. Does it seem to slip or jump when it does this? I know that there were issues with the torsion damper assembly on the input shaft, but I'm not certain which years were affected. The damper is basically a pair of spring loaded cams that take up driveline shocks. What can happen is it will rotate past the top of the cams due to a weakened spring. Since you describe it happening under heavy throttle application, it is a possibility.

[Andy VH]

For around town I make my 1st to 2nd shift quite a bit lower, like 2500 to 3000 especially if riding two up as it decreases the "whip" (helmet wack) result by my passenger. For accelerating up a highway entrance ramp 4000 to 5000 is a common shift rpm. If I'm riding two up I tend to short shift the lower gears and progressively shift at higher rpms up to 4th and 5th.

[kbasa]

I dunno. Torque peak on an RS is about 5000 rpm with the hp peak right at redline. I shift it well up, usually closer to redline. If I'm cruising around town, I'll short shift it at 4 or so, but if I want to go somewhere, I surf it between 3500 and the top.

75K or so on the ol' gal and she still loves to play.

Here are some plots from Factory Pro Tuning. They use an eddy current dyno, rather than a drum dyno like DynoJet uses. Power is measured at steady rpm, rather than the sweeping accelerative plots DynoJet uses, so measurements tend to look lower.

Wind it up!

http://kbasa.smugmug.com/photos/1247419_2T9Pw-L.jpg

[breyfogle]

The Clunk happens post shift when I then add throttle. If I bring the RPM up really (really!) slowly its all good, any rapid uptick and.... THUNK, big and heavy.

Does go THUNK every time you accelerate in 2nd gear or does it do it when you accelerate hard but not do it if you accelerate easily ?

I've had a similar sounding problem with my K75 for quite awhile. When it first began to act up, a hard up hill acceleration in second gear would sometimes result in what felt like a momentary false neutral as the tranny slipped out of second gear. This was followed very quickly by a loud drive-line BANG as second gear re-engaged itself. As the 2nd gear engagement dogs and/or the shifter fork continued to wear, 2nd gear has gradually become less and less able to handle acceleration torque and maintain engagement. If this fits your situation, begin saving your pennies for a trany rebuild.

[jerryjameson]

Does go THUNK every time you accelerate in 2nd gear or does it do it when you accelerate hard but not do it if you accelerate easily ?

I've had a similar sounding problem with my K75 for quite awhile. When it first began to act up, a hard up hill acceleration in second gear would sometimes result in what felt like a momentary false neutral as the tranny slipped out of second gear. This was followed very quickly by a loud drive-line BANG as second gear re-engaged itself. As the 2nd gear engagement dogs and/or the shifter fork continued to wear, 2nd gear has gradually become less and less able to handle acceleration torque and maintain engagement. If this fits your situation, begin saving your pennies for a trany rebuild.

That is a perfect description of how the problem manifests. At this point the bike still is ridable, albeit with a smooth hand into second.
Thanks.

Jerry